I had a similar problem on my 450. Mine is totally stock though. The truck wouldn't start when it was very hot outside. Everything worked inside the truck, but when I turned the key I got nothing, not even a click. called the dealer four times about it and they told me to make sure I was using the correct key...
Most times when it would happen, I could just wait 10 minutes and then it would start, but one time I had to leave the truck at work one night and came back in the morning and it started. I drove it straight to the dealer and it popped a code. Turns out the unit that receives the signal from the key was bad. No problems since.